The present invention relates to a process for producing a modified polymer rubber having superior impact resilience, which modified polymer rubber is accordingly capable of producing motorcar tires having superior fuel cost saving.
A styrene-butadiene copolymer obtained by emulsion polymerization is known as rubber used for motorcar tires. However, said copolymer has a problem that motorcar tires comprising said copolymer are not satisfactory from a view point of fuel cost saving, because the copolymer does not have sufficient impact resilience.
In order to obtain rubber having superior impact resilience, JP-B 5-46365 discloses a process, which comprises copolymerizing butadiene and styrene in a hydrocarbon solvent using an organolithium compound as an initiator, and a Lewis base such as ether as a microstructure controlling agent.
Further, Japanese Patent No. 2540901 proposes a process, which comprises reacting an alkali metal, which is bound at the end of a diene polymer rubber, with a specific acrylamide to obtain a modified diene polymer rubber having improved impact resilience.
However, recently, a level of a demand for fuel cost saving of motorcar tires is higher from an environmental view, and therefore, any of the above-mentioned copolymer rubbers can hardly meet such a demand.
An object of the present invention is to provide a process for producing a modified polymer rubber having superior impact resilience.
The present invention provides a process for producing a modified polymer rubber, which comprises the steps of:
(1) polymerizing a conjugated diene monomer, or the conjugated diene monomer and an aromatic vinyl monomer in the presence of an alkali metal catalyst in a hydrocarbon solvent to produce an active polymer having an alkali metal at its end(s), and
(2) reacting the active polymer with a ketone compound represented by the following formula (1) to produce a modified polymer rubber, 
wherein R1 is an alkyl group, an alkoxy group, a phenyl group or a benzyl group having 1 to 8 carbon atoms; and R2 is an N-substituted cyclic amino group.